For Russian Prime Minister Vladimir Putin, the U.S. is a “parasite” because its rising debt weighs on the global economy. For his government, the same debt is the safest possible investment.

Russia, the world’s largest energy producer, has boosted its holdings of U.S. debt by more than 1,600 percent since September 2006, according to U.S. Treasury Department data. Russia used surging commodity prices to build the world’s third- largest reserves pile, boosted in part by return on Treasuries.

Putin, 58, who oversaw the largest buildup of U.S. debt holdings in Russia’s history as president from 2000 to 2008, may return to the post after elections next year. The country is now one of the world’s 10 largest holders of the securities with $110 billion at the end of June, about 70 percent more than when Putin left the Kremlin.

“They are sending out a message” largely for domestic consumption, Edwin Gutierrez, who helps manage about $7 billion in emerging-market debt at Aberdeen Asset Management in London, said in a phone interview on Aug. 17. “It’s ironic that these voices of complaint come as they experience massive capital appreciation.”